The present invention relates to a liquid crystal display device, and more particularly to an active matrix liquid crystal display device operable with an in plane switching mode and a method of driving the same.
It has been known that one of active material liquid crystal display devices is operable in in-plane switching mode, wherein liquid crystal molecules are switched in horizontal direction by applying an electric field to the liquid crystal molecules in the horizontal direction. The electric field is generated between two electrodes formed in a substrate in which thin film transistors are formed. This in-plane switching mode active material liquid crystal display device has, for example, been used for displays or monitors of computers such as note-type personal computers.
FIG. 1 is a circuit diagram illustrative of an equivalent circuit of a first conventional in-plane switching mode active material liquid crystal display device. The first conventional in-plane switching mode active material liquid crystal display device comprises a data driver circuit 1510, a gate driver circuit 1520 and a liquid crystal display panel 1530 which is connected to the data driver circuit 1510 and the gate driver circuit 1520. The liquid crystal display panel 1530 has an array of pixels 1540 which are aligned in matrix throughout the liquid crystal display panel 1530. The liquid crystal display panel 1530 also has a plurality of data lines 1531 which extend in parallel to each other in a first direction for transmission of data to the pixels 1540. The data lines 1531 are connected to the data driver circuit 1510. The liquid crystal display panel 1530 also has a plurality of gate lines 1533 which extend in parallel to each other but in a second direction perpendicular to the first direction along which the data lines 1531 extend. The gate lines 1533 are provided for transmission of gate control signals to the pixels 1540. The gate lines 1533 are connected to the gate driver circuit 1520. The pixels 1540 are positioned at crossing points of the data lines 1531 and the gate lines 1533. The liquid crystal display panel 1530 also has a single column-common electrode line 1532 which extends in parallel to each other but in the first direction perpendicular to the second direction along which the gate lines 1533 extend.
Each of the pixels 1540 is represented by a square-shaped broken line in FIG. 1. Each of the pixels 1540 further comprises a pixel transistor 1541, a storage capacitor 1542, a pixel electrode 1543 and a column-common electrode 1544. The pixel transistor 1541 comprises a thin film transistor formed in a substrate. The pixel transistor 1541 in each of the pixels 1540 has a gate electrode which is connected to corresponding one of the gate lines 1533. The pixel transistor 1541 in each of the pixels 1540 has a source electrode which is connected to corresponding one of the data lines 1531. The storage capacitor 1542 is connected between a drain electrode of the pixel transistor 1541 and a ground line. The pixel electrode 1543 in each of the pixels 1540 is connected to the drain electrode of the pixel transistor 1541. The column-common electrode 1544 in each of the pixels 1540 is connected to the single column-common electrode line 1532, so that an external voltage may be applied through the single column-common electrode line 1532 to the column-common electrode 1544 in each of the pixels 1540. The data lines 1531 are driven by the data driver circuit 1510. The gate lines 1533 are driven by the gate driver circuit 1520.
FIG. 2 is a timing chart illustrative of waveforms of a horizontal synchronizing signal Hsync, a column-common electrode potential Com, a first data line potential D1 of first one of adjacent two data lines, a second data line potential D2 of second one of the adjacent two data lines, a first gate line potential G1 of first one of adjacent two gate lines, and a second gate line potential G2 of second one of the adjacent two gate lines to explain the driving method of the first conventional in-plane switching mode active material liquid crystal display device of FIG. 1.
The following descriptions are operations of writing image signals into pixels of the first conventional in-plane switching mode active material liquid crystal display device of FIG. 1. Pulse signals are sequentially outputted from output terminals of the gate driver circuit 1520 in synchronizing with the horizontal synchronizing signals Hsync of the image signal. The data driver circuit 1510 is operated to fetch the image signals with one horizontal time period unit in order to output the image signals onto the data lines 1531. Each pulse signal outputted from the gate driver circuit 1520 is transmitted on one of the gate lines 1533, whereby the pixel transistor 1541 having the gate electrode connected to the one of the gate lines 1533 turns ON, during which an image signal voltage Vvc outputted from the data driver circuit 1510 is applied through the pixel transistor 1541 into the pixel electrode 1543. On the other hand, a column-common voltage Vcom is applied to the column-common electrode 1544 through the single column-common electrode line 1532. Namely, the pixel electrode 1543 has the image signal voltage Vvc, whilst the column-common electrode 1544 has the column-common voltage Vcom. A potential difference of Vvcxe2x88x92Vcom is generated between the pixel electrode 1543 and the column-common electrode 1544. Namely, the pixel 1540 has the potential difference of Vvcxe2x88x92Vcom, which generates an electric field to be applied to liquid crystal molecules positioned between the pixel electrode 1543 and the column-common electrode 1544. The liquid crystal molecules are therefore switched.
The foregoing operations are repeated for one frame unit thereby to obtain a two-dimensional image.
The image signals to be applied to the pixel electrode are required to be changed in polarity with reference to the column-common electrode potential in every frame units. Namely the polarity inversion driving is carried out to the data driver circuit 1510 in order to obtain or secure a highly accurate intensity of the electric field applied to applied to the liquid crystal molecules. By contrast to the polarity inversion driving, if a direct current electric field would be applied to the liquid crystal molecules, an electrolysis of the liquid crystal molecules is caused to generate ions in the liquid crystal molecules, whereby the generated ions generate local electric fields which displaces the intensity of the electric field applied between the pixel electrode and the column-common electrode.
The above described in-plane switching mode active matrix liquid crystal display requires a higher driving voltage by 6 V than that of a twisted nematic mode active matrix liquid crystal display. In order to accomplish the polarity inversion driving, a high voltage of not less than 12 V is required to be applied to the liquid crystal panel.
Further, it is required for realizing intermediate gray scale display of full color with 256-gray scales that the accuracy of the voltage level applied to the pixel electrode is within xc2x1several tens mV. The data driver circuit 1510 is required to have a high quality performance like that an output voltage range is not less than 12 V, and an error in voltage level of the output voltage is within xc2x1several tens mV.
If the display is applied to the liquid crystal display panel having a resolution of extended graphics array (1024xc3x97768), the number of the output terminals of the data driver circuit is not less than 1024. It is thus required to suppress variations in output voltage level of those output terminals within xc2x1several tends mV.
The above described conventional in plane switching mode active matrix liquid crystal display has he following problems.
The first problem is that it is quite difficult to design the data driver circuit having a large number of output terminals but is capable of highly accurate control to error of the output voltage level within xc2x1several tends mV.
The second problem is that the polarity inversion driving requires application of a large voltage of two times of the signal voltage level to the pixel, whereby a consumed power of the data driver circuit is large.
In the above circumstances, it had been required to develop a novel in plane switching mode active matrix liquid crystal display device free from the above problems.
Accordingly, it is an object of the present invention to provide a novel in plane switching mode active matrix liquid crystal display device free from the above problems.
It is a further object of the present invention to provide a novel in plane switching mode active matrix liquid crystal display device which is capable of applying a highly accurate voltage level to a liquid crystal even if an off-set of an amplifier of a data driver circuit is varied.
It is a still further object of the present invention to provide a novel in plane switching mode activc matrix liquid crystal display device which is capable of reducing an operating amplitude voltage of the data driver circuit to reduce a power consumption.
It is yet a further object of the present invention to provide a novel in plane switching mode active matrix liquid crystal display device which is capable of reducing flicker.
It is an another object of the present invention to provide a novel method of driving an in plane switching mode active matrix liquid crystal display device free from the above problems.
It is further another object of the present invention to provide a novel method of driving an in plane switching mode active matrix liquid crystal display device which is capable of applying a highly accurate voltage level to a liquid crystal even if an off-set of an amplifier of a data driver circuit is varied.
It is still another object of the present invention to provide a novel method of driving an in plane switching mode active matrix liquid crystal display device which is capable of reducing an operating amplitude voltage of the data driver circuit to reduce a power consumption.
It is yet another object of the present invention to provide a novel method of driving an in plane switching mode active matrix liquid crystal display device which is capable of reducing flicker.
The present invention provides a data driver circuit for an active matrix liquid crystal display device having an array of pixels aligned in matrix, and each column of the pixels having a pair of a separate data line and a separate column-common line which are separated from any other columns, wherein the data driver circuit has a plurality of selectors, each of which is connected to corresponding one of plural sets of the separate data line and the separate column-common line, so that each of the selectors selects any one of a first transmission of image signals through the selector to the data line and a second transmission of at least one column-common voltage onto the separate column-common line
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.